1. Field of the Invention
The present invention relates generally to radially expansible intraluminal prostheses, such as grafts, stents, stent-grafts and the like. More particularly, the invention provides a flexible stent structure for delivery through irregular or curved body lumens in the vasculature, and for deployment at a target site in a tortuous body lumen. The stent structure may also have a plurality of axially extending anchor members for securing the stent structure to the luminal wall at the target site.
Luminal prostheses, commonly known as grafts, stents or stent-grafts, are tubular-shaped devices which function to hold open a segment of a blood vessel or other anatomical lumen. These stent-grafts, stents and grafts are provided for a variety of medical purposes. For example, stents can be placed in various body lumens, such as blood vessels and the ureter, urethra, biliary tract and gastrointestinal tract, for maintaining patency. Stents are particularly suitable for supporting dissections in the arterial tissue that may occur during, for example, balloon angioplasty procedures. Such dissections can occlude an artery and prevent the flood of blood therethrough. In addition, stents may be used to support grafts to form a stent-graft for lining or replacing weakened blood vessels, such as in aortic aneurysm repair procedures (e.g., aneurysms occurring in the abdominal aorta, usually beginning below the renal arteries and often extending distally into one or both of the iliac arteries).
An important consideration in deploying stents in the vasculature is the ability of the stent to anchor into the vessel to hold open the vessel and to prevent migration of the stent due to loads applied to the stent. Once deployed, the stent may be subjected to a variety of loads, such as blood flowing through the stent or the expansion and contraction of the blood vessel from the patient's heart beat. One of the mechanisms for anchoring a stent to a vessel is the outward radial force applied by the stent against the luminal wall after the stent has expanded to its final enlarged diameter within the body lumen. Unfortunately, it is often difficult to accurately predict the degree of radial force that will be exerted by an individual stent once it has been deployed and expanded within the patient's vasculature. A relatively low radial force exerted against the luminal wall may allow the stent to migrate along the body lumen and/or fail to adequately maintain lumen patency. This could cause potential injury to the patient and often requires another surgical procedure to remove the failed stent and deploy a second stent at the same portion of the diseased vessel or to effect surgical repair of the vessel. On the other hand, a relatively high radial force may potentially damage the luminal wall, e.g., by causing abnormal vessel distention or contributing to aneurysmal growth.
Another important consideration in deploying and implanting stents is the ability of the stent to pass through curvatures, bend and other irregularities within the body passageways during deployment, and to conform a tortuous body lumen at the target site after the stent has been implanted. Many stents and stent-grafts, particularly those which are relatively rigid, do not have the requisite ability to bend so as to conform to the curves and bends present within the vasculature. To overcome this deficiency, recent stents have been manufactured from a plurality of rigid tubular rings that are connected to each other with flexible connecting structures, such as hinges, springs or the like. The flexible connecting structures allow adjoining rigid rings to pivot relative to each other so that the entire stent may flex along its length within the delivery catheter. Although these recent stents have some ability to conform to and to negotiate curves and bends, they still present deployment problems. For example, the rigid tubular rings may become stuck or jammed as the connecting structures bend around curves in the body passageway. Often, the surgeon must apply force to the delivery catheter to urge the catheter and the stent around the curve and continue its progress through the body passageway. This hinders the deployment process, and may injure the luminal wall. In addition, these rigid tubular rings generally do not conform well to a tortuous body lumen at the target site, which can cause performance problems after the stent has been deployed.
For these and other reasons, it would be desirable to provide methods and apparatus for securely anchoring stents, grafts or stent-grafts to luminal walls after the stent has expanded within the body lumen to decrease migration and/or failure of the stent. It would be further desirable to provide stents with a geometry and sufficient flexibility such that the stents conform to curves and bends in the patient's vasculature to facilitate deployment of the stent at the target site, and to enhance the performance of the stent after it has been implanted.
2. Description of the Background Art
U.S. Pat. Nos. 5,104,404 to Wolff, 5,443,496 to Schwartz and 5,195,984 to Schatz each describe an articulated stent having a number of rigid stent segments connected together with flexible hinges, such as wire, or coiled wire. The stent segments each generally comprise a plurality of V-shaped elements connected together. U.S. Pat. No. 5,449,373 to Pinchasik describes an articulated stent with a plurality of substantially rigid segments coupled together with flexible connectors having one or more kinks for advancing through curved body lumens. U.S. Pat. No. 5,282,824 to Gianturco describes a self-expanding stent having a plurality of Z-stents connected together and covered by a flexible nylon sleeve. European Patent Application 540 290 A2 to Advanced Cardiovascular Systems, Inc. discloses an expandable stent made up of a plurality of radially expandable cylindrical elements interconnected by axial elements. The stent is formed by removing exposed portions of a tubing by an etching process. U.S. Pat. No. 5,102,417 to Palmaz illustrates an expandable vascular graft having thin-walled tubular members with a plurality of longitudinal slots. The tubular members are connected together with flexible spiral connectors.